With the progress of computer technology, video game machines (picture processing devices) utilizing computer graphic technique have come to be widely used. Particularly, popularity of video game machines which imitate ball games such as baseball or soccer has been firmly established, and a considerable amount of this type of video game machines have been devised.
However, conventional video game machines have many problems as described below.
First, it is difficult to display a fielder's ball-catching movement smoothly.
A conventional video game machine generally comprises: a display which displays batters, fielders and other characters; an operation stick which operates batters, fielders and other characters on a screen; and a picture processing circuit which displays a desirable image on the screen in accordance with the operation of the operation stick. Such a video game machine is provided with a plane picture called "sprite" for each movement posture of each fielder, and the sprite is displayed according to the progress of a game on the screen. A virtual area called the "collision area" for determination of collision is provided in the vicinity of a fielder. When a ball enters the collision area, the fielder moves to catch the ball.
For example, when a game player operates the stick, the fielder on the screen chases the batted ball in accordance with the operation of the stick. The collision area, then, also moves together with the fielder. If the fielder catches up with the ball and the ball enters the collision area near the fielder, the fielder moves to catch the ball. Namely, the video game machine determines that the ball in the screen has reached close to the fielder, and displays the sprite which shows the ball-catching movement. Therefore, the fielder never begins the ball-catching movement unless the ball enters the collision area on the screen.
However, since the time spent after the ball enters the collision area until the fielder catches the ball is very short, the fielder needs to perform the ball-catching movement in a very short period of time after the ball enters the collision area. Accordingly, the fielder's ball-catching movement turns out to be awkward and it is then difficult to provide a realistic game. As a means for solving this problem, it is possible to enlarge the collision area near the fielder. In other words, it is possible to lengthen the time spent after the ball enters the collision area until the fielder catches the ball. However, if the collision area is enlarged, a problem arises that the fielder begins moving to catch a ball even when the ball is too far away to catch.
Secondarily, a considerable amount of operation is required for a processing which determines the collision between a batted ball and a fence, which subsequently hinders high speed processing.
When a batted ball flies beyond an outfielder in a video game machine, whether or not a collision will take place between the batted ball and the fence is determined. For example, when the fence is displayed with a plurality of polygons, it is determined whether or not coordinates of the ball are located on the polygons. If it is determined that the ball will collide with the polygons which compose the fence, a processing for bounding the ball back from the fence is performed.
Namely, the conventional baseball game determines whether the ball collides with the fence by confirming whether coordinates of the ball are positioned on the polygons which compose the fence. However, since coordinates of the ball and the polygons are expressed by three-dimensional data, a considerable amount of processing is required to determine the position relationship between the ball and the polygons. Therefore, there existed a problem in that a processing speed of the entire game was lowered.
Thirdly, it is difficult to accurately perform a hidden face treatment of polygons which are located very close to each other as in the case of a player's number and a uniform.
In video games such as baseball and soccer, it is desirable to give different player's numbers for different players in order to heighten the realistic excitement of the game. However, if different pictures are prepared for uniforms of different players, an enormous amount of display data would be required. Therefore, a method of preparing a picture of the uniform and a picture of the player's number separately and superimposing the picture of the player's number on the picture of the uniform is taken.
However, when the player's number and the uniform are displayed by means of polygons, the following problems occur. When the polygons overlap one another, a treatment is performed not to display the overlapped portion of the polygons, which is positioned at the back of the other overlapped portion on the screen ("hidden face treatment"). In order to perform this hidden face treatment, the following method ("Z-sorting method") is suggested: priority of respective polygons is determined in accordance with the dimensions of depth-directional coordinates (z-coordinate values) of the polygons, and the polygons are displayed in accordance with the priority. Namely, in the Z-sorting method, a representative point is decided for each polygon and the priority of the polygons is determined in accordance with the dimensions of z-coordinate values of the representative points.
As described above, one representative point must be decided for each polygon when the Z-sorting method is employed. In order to decide a representative point, there are: a method of determining the most front vertex among vertexes of a polygon as its representative point; a method of determining the most back vertex among vertexes of a polygon as its representative point; and a method of determining the center of gravity of a polygon as its representative point. However, whichever method is taken, if two polygons, such as those of a player's number and a uniform, are located very close to each other, in other words, if two sets of z-coordinate values are very close, it is difficult to accurately determine the priority of the polygons. Accordingly, a problematic hidden face treatment is sometimes performed: for example, a player's number is hidden by a uniform.
In order to avoid such a problem, it is possible to give a higher priority to a player's number than to a uniform and to always superimpose the player's number on the uniform. However, this method could cause another problem that when a fielder faces front so that his back is not displayed, his number is still displayed. Accordingly, it has been difficult to accurately apply the hidden face treatment to polygons which are located very close to each other.
The present invention is devised in order to overcome the above-described problems. The first object of this invention is to provide a picture processing device and a method thereof which enable a smooth ball-catching movement.
The second object of this invention is to provide a picture processing device and a method thereof which make it possible to determine a collision between a batted ball and a fence by means of a simple operation.
The third object of this invention is to provide a picture processing device and a method thereof which make it possible to accurately apply the hidden face treatment to polygons which are located very close to each other such as a player's number and his uniform.